FIG. 1 shows an OLED device 100 which serve, for example, as a display in various types of consumer electronic products, including cellular phones, cellular smart phones, personal organizers, pagers, advertising panels, touch screen displays, teleconferencing and multimedia products, virtual reality products, and display kiosks.
The OLED device comprises a functional stack formed on a substrate 101. The functional stack comprises of one or more organic functional layers between two conductive layers which serve as electrodes (cathode and anode). The conductive layers are patterned to form rows of cathodes in a first direction and columns of anodes in a second direction. OLED pixels are located where the cathodes and anodes overlap. Charge carriers are injected through the cathodes and anodes via bond pads 150 for recombination in the functional layers. The recombination of the charge carriers causes the functional layer of the pixels to emit visible radiation.
The device is encapsulated with a cap 160, sealing pixels. OLED devices require hermetic sealing since the active components, such as the cathode, are adversely impacted by moisture and oxygen. Typically, an epoxy based adhesive is used to bond the cap to the substrate. However, epoxy based adhesive can be penetrated by oxygen and moisture. The penetration path of the oxygen and moisture is along the interface 180 of the cap and substrate. The length of the penetration path is defined by the bonding width W. The rate of penetration of oxygen and moisture Q depends on the bonding thickness T and W. The rate Q is directly related to the bonding thickness T and inversely related to the bonding width W. Since there is a limit to how much the bonding thickness can be reduced, extending the shelf life of the OLED device is achieved by lengthening the penetration or permeation path which corresponds to increasing the bonding width. Increasing the bonding width undesirably increases the dimension of the device unnecessarily.
As evidenced from the foregoing discussion, it is desirable to provide improved sealing of OLED device without unnecessarily increasing its dimensions.